In the conventional method of pureeing fruit or vegetable products, the product is first peeled and then macerated or crushed. The macerated product is then separated, to separate the puree from the seeds and fiber. This latter step normally takes place in a pulper-finisher or a centrifuge. The puree is then preserved by freezing, pasteurization, sterilization, or the like.
Although heat is sometimes used during the normal pureeing process, enzymes released during maceration act so quickly that undesirable off-flavor, color destruction, browning, and nutrient loss occurs before the heat can inhibit the enzyme activity. On the other hand, if whole fruit is blanched before maceration, heat penetration is so slow that it may initially activate the enzymes before the heat rises to inhibition temperatures. Heat penetration into whole fruit or vegetables is relatively slow, and the time for full heat penetration is so long as to actually initiate enzyme activity even within the cellular structure of the product before inhibition occurs.
Another disadvantage of heating whole fruit or vegetables is that by the time the product is maintained under heat long enough to insure full penetration to the center, the outer portions of the product may be cooked or semi-cooked, thus producing an inferior product.